1. Field of the Invention
The present invention relates to a communication system in which a plurality of devices perform communications through a network, and particularly relates to a communication system having such functions of preventing a communication failure from occurring and providing information for identifying a location of failure in the case where the communication failure occurs.
2. Description of the Related Art
An image special effect apparatus or a switcher is used to apply a special effect to a video signal at a video production site such as a television broadcasting station. The switcher is configured to have one or more video processing units (matrix switcher, mixer/keyer, and DME), which is a switcher main unit, and an operation input unit for operating the video processing units.
As shown in FIG. 1, as a connection mode for exchanging a control command and device status information between the operation input unit and respective video processing units and between the respective video processing units, there is typically provided such a mode that an operation input unit 51 and respective video processing units 52 and 53 are connected in a star LAN (Local Area Network) using a hub 54.
In the case of the above connection mode, the connections are respectively established between the operation input unit and video processing units and between the respective video processing units in accordance with TCP/IP protocol. The control command and device status information are exchanged at a period of one field in which a video signal is input into the video processing unit (for example, once every 16.7 msec in the case of NTSC, and once every 20 msec in the case of PAL).
In the case where the exchange of the control command and device status information is disrupted for one second or longer, the TCP/IP connection is once cancelled and then the connection is reestablished. While the connection is not established, it may not be possible to control the video processing unit from the operation input unit.
In the past, when the connection is not established or the connection is not maintained for a long time, more specifically, when there occurs such failure that the operation input unit is unable to control the video processing unit, it has been difficult to identify the cause thereof. Specifically, it is difficult even using measuring instrument to determine whether a failure is caused in the device of the switcher, such as the operation input unit and the video processing unit, or caused in the LAN (such as the hub).
However, since the switcher is an apparatus in which the video processing unit may need to be controlled in real-time by an operation of the operation input unit, it is inconvenient if the control is interrupted even temporarily. Therefore, it may be required to identify the cause of such communication failure and correct the failure and furthermore to prevent such failure from occurring by detecting a location where the communication failure is likely to occur.
In the past, various apparatuses have been proposed as an apparatus for monitoring traffic on the network (refer to Japanese Unexamined Patent Application Publication No. H11-177549, for example), however, there has not been proposed such apparatus having functions of preventing a communication failure from occurring and providing information for identifying the location of failure in the case where the communication failure occurs.